1. Technical Field
The present invention relates to a power supply device that includes a substrate, a transformer, a rectifying section, and a filtering section.
2. Related Art
An example of a technology related to switching power supply devices is disclosed (for example, refer to JP-A-2002-209383). An object of the technology is to reduce switching loss by soft switching and to reduce circulating current loss. The switching power supply device includes a snubber. The snubber is connected in parallel with a rectifying element. The rectifying element is connected to a secondary side of a transformer. The snubber includes a snubber capacitor. A diode or a semiconductor switch element, such as an insulated-gate bipolar transistor (IGBT), is used as the rectifying element.
The snubber capacitor is connected in parallel with the rectifying element. As a result, surge voltage that is generated when the rectifying element is turned OFF can be suppressed. However, resonance is generated as a result of the leakage inductance component of the transformer and the capacitance component of the snubber capacitor. In accompaniment with the generation of resonance, the peak value (maximum value of amplitude; the same applies hereafter) of the surge voltage may exceed the rating of a circuit element.
To suppress the peak value of surge voltage, a method may be considered in which the capacitance of the snubber capacitor is increased. However, as the capacitance increases, problems occur such as increase in the current flowing to the snubber capacitor, increase in the amount of heat generated by the snubber capacitor, and reduced power efficiency.